In downhole operations, it is common to treat various segments of the wellbore independently. For example, cementing casing within the wellbore may be completed in various stages, using isolation equipment and valves to direct cement about the casing annulus in successive segments. Similarly, in completion operations, various zones of the wellbore may be perforated independently and treated independently.
Wellbore zones are commonly isolated by strategic placement of bridge plugs, cup seals, inflatable sealing elements, and compressible elements, which may be appropriately positioned either inside a cemented casing, or outside an uncemented liner.
Various means to provide isolated access to the formation are known, which commonly include perforation of the casing or liner, or by otherwise providing ports within the liner. Within an isolated zone, the hydraulic pressure about the tool string may fluctuate based on the treatment being applied to the zone. In some operations, it may be desirable to quickly dissipate the annulus pressure when a certain threshold of pressure is reached.